1. Technical Field
This invention relates to polymer blends, and more particularly it relates to blends of polyethylene copolymers. In another aspect this invention relates to transdermal drug delivery devices and to backings for use in such devices. This invention also relates to extruded films.
2. Description of the Related Art
Transdermal drug delivery is an increasingly important method of drug administration. Transdermal drug delivery devices typically involve a carrier (such as a liquid, gel, or solid matrix, or a pressure sensitive adhesive) into which the drug to be delivered is incorporated. The drug-containing carrier is then placed on the skin and the drug, along with any adjuvants and excipients, is delivered to the skin.
Typically the portions of the carrier that are not in contact with the skin are covered by a backing. The backing serves to protect the carrier (and the components contained in the carrier, including the drug) from the environment and prevents loss of the ingredients of the drug delivery device to the environment. Because hydration of the stratum corneum is known to enhance transport of certain drugs across the skin, it is sometimes desirable that the backing have a relatively low moisture vapor transmission rate in order to retain moisture at the site covered by the drug delivery device. In order to maintain the health of the covered skin during long term wear (e.g., for periods in excess of a day) by allowing the skin to breath, it is also desirable that the backing have relatively high permeability to oxygen. Further, as the backing is in contact with the components of the carrier, including the drug and any adjuvants and excipients, it is important that the backing be stable to such components in order that the backing retain structural integrity, tensile strength, and conformability to the skin. It is also important that the backing not absorb drug or other excipients from the carrier. In connection with the preparation of certain reservoir-type transdermal drug delivery devices, it is also desirable for the backing to be heat sealable at a relatively low temperature to itself and to a variety of other polymeric substrates.
Backing materials that have found use in transdermal drug delivery devices include metal foils, metalized plastic films, and single layered and multilayered polymeric films. Deficiencies of these backings that are occasionally manifest include delamination of multilayered polymeric films, oxygen impermeability of metal foils, metalized plastic films, and certain polymeric films, instability of certain polymeric materials to the components of the carrier, and absorption of components from the carrier by certain polymeric materials. Also, it is known that certain polymeric materials are difficult to handle and process into suitable films.